Implantable therapy systems and methods

ABSTRACT

Implantable therapy systems are disclosed for the local and controlled delivery of a biologically active factor to the brain, spinal cord and other target regions of a subject suffering from a debilitating condition. The method of the invention involves surgically exposing an insertion site, generally located above a predetermined treatment site (12), in a patient. A cannula (20), having an obturator (30) or dilator (104) positioned therein, is inserted at the insertion site, defining a pathway to the treatment site. In some instances, the cannula can be inserted along the path of a guidewire (102) previously positioned at the treatment site. The cannula (20) is preferably a low friction polymeric material such as polytetrafluoroethylene. The cannula (20) generally has an open proximal end for receiving the obturator (30) or dilator (104), and an open distal end, preferably a tapered end, for delivery of neurologically active factors to the treatment site (12). The obturator (30) is then removed from the cannula (20), and a biocompatible tethered vehicle (40) containing a biologically active material is inserted into the cannula along the passageway. A pusher can be inserted within the cannula, behind the vehicle (40), to position the proximal end of the vehicle at the distal end of the cannula (20b). Once the vehicle (40) is positioned near the distal end of the cannula (20), the cannula is removed from the passageway, followed by the pusher, leaving the vehicle (40) positioned at the treatment site (12).

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 07/998,368, filed Dec.30, 1992, entitled IMPLANTABLE THERAPY SYSTEMS AND METHODS nowabandoned, which is a continuation-in-part of U.S. patent applicationSer. No. 722,947 filed Jun. 28, 1991, entitled "Neural Implant Methodand System" now abandoned, which is a continuation-in-part of U.S.patent application Ser. No. 369,296 filed Jun. 21, 1989 now abandoned,entitled "Neurological Therapy Devices", which is a continuation-in-partof U.S. patent application Ser. No. 121,626, filed Nov. 17, 1987,entitled "In vivo Delivery of Neurotransmitters by Implanted,Encapsulated Cells", now U.S. Pat. No. 4,892,538.

BACKGROUND OF THE INVENTION

The technical field of this invention includes the treatment ofneurological disorders and treatment of acute and/or chronic pain. Inparticular, the invention concerns the treatment of diseases anddisorders which may be remedied by treatment with secretory substances,such as neurotransmitters, neuromodulators, hormones, trophic factors,or growth factors, as well as the reduction of pain sensitivity by theprovision of a sustained local delivery of neuroactive substances,particularly catecholamines and opioid peptides. All these substancesare characterized by the fact they are secreted by "source" cells andproduce a specific change in the source cell itself or in a "target"cell (i.e., they are biologically active).

Deficits in secretory substances have been implicated in variousneurological diseases. Lack of neurotransmitter-mediated synapticcontact causes neuropathological symptoms, and can also lead to theultimate destruction of the neurons involved.

For example, paralysis agitans, more commonly known as Parkinson'sdisease, is characterized by a lack of the neurotransmitter, dopamine,within the striatum of the brain, secondary to the destruction of thedopamine secreting cells of the substantia nigra. Affected subjectsdemonstrate a stooped posture, stiffness and slowness of movement, andrhythmic tremor of limbs, with dementia being often encountered in veryadvanced stages of the disease.

The direct administration of purified or synthetic dopamine, itsprecursors, analogs and inhibitors has been studied for therapeuticvalue in the treatment of Parkinson's disease. These studies haverevealed various problems with delivery, stability, dosage, andcytotoxicity of the applied compounds. To date, none of these approacheshas demonstrated more than marginal therapeutic value. Brain derivedgrowth factor also may have potential value in the treatment ofParkinson's disease since it has been demonstrated to maintain theviability of striatal neurons in vitro.

Many other diseases, especially neurological disorders appear to bebased in whole, or in part, on the absence or limited availability, totarget cells or regions, of a critical biological factor.

It is also fairly well established that the activation of noradrenergicor opioid receptors in the spinal cord by direct intrathecal injectionof α-adrenergic or opioid agonists produces antinociception, and thatthe co-administration of subeffective doses of these agents can producepotent analgesia. The presence of enkephalin-secreting neurons andopiate receptors in high densities in the substantia gelatinosa of thespinal cord and the resultant analgesia observed following localinjection of opiates into the spinal cord have suggested a role foropioid peptides in modulating the central transmission of nociceptiveinformation. In addition, catecholamines also appear to be important inmodulating pain sensitivity in the spinal cord since injection ofnoradrenergic agonists into the subarachnoidal space of the spinal cordproduces analgesia, while the injection of noradrenergic antagonistsproduces increased sensitivity to noxious stimuli.

In an attempt to provide a continuous supply of drugs or other factorsto the brain and other tissues at a controlled rate, miniature osmoticpumps have been used. However, limited solubility and stability ofcertain drugs, as well as reservoir limitations, have restricted theusefulness of this technology. For example, controlled sustained releaseof dopamine has been attempted by implanting dopamine encapsulatedwithin bioresorbable microcapsules (McRae-Degueurce et al. (1988)Neurosci. Lett. 92:303-309). However, controlled sustained release of adrug from a bioresorbable polymer may rely, e.g., on bulk or surfaceerosion, which may be due to various hydrolytic events, increasing thelikelihood of drug degradation, and rendering predictable release ratesdifficult. Others may be limited to finite loading of the polymer, andmay lack any cellular feedback regulation.

Many drugs have been administered intraspinally in the clinical setting,and numerous methods are available to deliver intraspinal medications.For instance, the most common method of intraspinal drug delivery,particularly anesthetics, is continuous infusion by way of spinalcatheters. However, the use of these catheters, particularly small-borecatheters, has been implicated in such complications as cauda equinasyndrome, a neurological syndrome characterized by loss of sensation ormobility of the lower limbs. In fact, the FDA was prompted to issue asafety alert in May, 1992, alerting Anesthesia Care Providers to theserious hazard associated with continuous spinal anesthesia bysmall-bore catheters and has taken action to remove all small-borecatheters from the market.

The implantation of cells capable of constitutively producing andsecreting neuroactive factors has also been attempted. Recently,remedial transplantation of neurotransmitter-secreting tissue has beenaccomplished using the patient's own tissue so as not to elicit animmune response. For example, dopamine-secreting tissue from the adrenalmedulla of patients suffering from Parkinson's disease has beenimplanted in their striatum with some success. However, this procedureis only used in patients less than 60 years of age, as the adrenal glandof older patients may not contain sufficient dopamine-secreting cells.This restriction limits the usefulness of the procedure as a remedysince the disease most often affects older people. A further problemassociated with this procedure is that it requires an additional,distinct surgical procedure.

Other transplantation approaches have demonstrated that even though theCentral Nervous System (CNS), e.g. the brain and spinal cord, isconsidered "immuno-privileged", rejection ultimately occurs with bothallografts and xenografts. This problem necessitates theco-adminstration of immuno-suppressors, the use of which renders theirown set of complications and deleterious side-effects. For example,human medullary tissue has been implanted into the subarachnoid space ofpatients suffering from terminal cancer and has been shown to reduceboth acute and chronic pain. However, the limited availability of humandonor tissue for allografts reduces the potential for its large scaleuse, suggesting the need to utilize xenographic donors. It is clear thatthe use of widely disparate histoincompatible species (i.e. bovine andhuman) can result in severe immunological responses, which can cause theultimate destruction of the graft. The immunosuppresent cyclosporine Ahas been used to prolong bovine adrenal medullary chromaffin cellxenografts in the rat CNS, but survival is variable and cyclosporine Acan be toxic with potentially serious complications includinghepatotoxicity and nephrotoxicity, as well as tumorogenicity. Withregard to the use of cyclosporine A in humans, the serious side effectsassociated with its use have precluded its administration to otherwisehealthy patients.

A number of researchers have proposed the use of microcapsules, i.e.,tiny spheres which encapsulate a microscopic droplet of a cell solution,for both therapeutic implantation purposes and large scale production ofbiological products. However, there are a number of shortcomings to themicroencapsulation approach. For example, the microcapsules can beextremely difficult to handle, including being difficult to retrieveafter implantation. The types of encapsulating materials which can beused are constrained by the formation process to polymers which candissolve in biocompatible solvents. Furthermore, due to the limiteddiffusional surface area per unit volume of larger size spheres, only alimited amount of tissue can be loaded into a single microcapsule.

An alternative approach has been macroencapsulation, which typicallyinvolves loading cells into hollow fibers and then sealing theextremities. In contrast to microcapsules, macrocapsules offer theadvantage of easy retrievability, an important feature in therapeuticimplants, especially neural implants. However, the construction ofmacrocapsules in the past has often been tedious and labor intensive.Moreover, due to unreliable closure, conventional methods ofmacroencapsulation have provided inconsistent results.

Therefore, there exists a need for improved therapies for the treatmentof neurological and other disorders in general, and in particular, aneed for therapy devices which can augment or replace the functions ofdysfunctional areas of the brain or other organs without causingexcessive trauma. There also exists a need for improved therapy toalleviate pain, particularly in the form of sustained analgesic deliverysystems. More specifically, there exists a need for a method ofproviding active, neuroactive factor to a localized region of thenervous system of a subject, the correct dosage of which will beconstitutively delivered over time.

Accordingly, it is an object of the present invention to provide animplantable, retrievable therapy device useful for the sustained andcontrolled delivery of a biologically active factor to a subject, andmore particularly, to provide a device which can deliver a biologicallyactive factor, e.g., a neuroactive factor or growth factor, to alocalized region in the CNS of a subject.

SUMMARY OF THE INVENTION

Neurological therapy methods and systems are disclosed for the local andcontrolled delivery of a biologically active factor to the brain, orother portion of the CNS, or other organ of a subject. The methods andsystems are useful for treating subjects suffering from a deficiency ororgan dysfunction, or suffering from acute and/or chronic pain.

A method of the invention involves surgically exposing an insertion sitegenerally located above a predetermined treatment site, which site maybe within brain tissue or other target organ tissue. The preciselocation of the treatment site, and the subsequent insertion sitelocation may be stereotaxically ascertained. A cannula, having anobturator positioned therein, is inserted at the insertion site,defining a passageway to the treatment site. The cannula generally hasan open proximal end for receiving the obturator, and an open distal endfor delivery of biologically active factors to the treatment site.

The method further involves removing the obturator from the cannula oncethe passageway is defined and the cannula is in the desired position.After the obturator is removed, a biocompatible vehicle containing abiologically active factor is inserted into the cannula along thepassageway. Once the vehicle is positioned near the distal end of thecannula, the cannula is removed from the passageway, leaving the vehiclepositioned at the treatment site.

The obturator may be re-inserted into the cannula after the vehicle isinitially placed in the cannula to position the vehicle at the distalend. This may be necessary if, for example, the vehicle does notslidably fit within the cannula. The obturator used for thus positioningthe vehicle may be the same as or different from the obturator initiallypositioned in the cannula. If an obturator is used to position thevehicle, it is removed following removal of the cannula to furtherassist in retaining the desired position of the vehicle at the treatmentsite.

Another form of the invention involves making an insertion site proximalto the treatment site, and introducing a guidance needle, optionallywith an obturator positioned in its central bore, into the area of thetreatment site. The needle lumen is opened by removing the obturator ifany is present, and a guidewire is introduced into the lumen of theneedle and is fed through until it enters the treatment site. Once theguidewire is contacting the treatment site, the guidance needle isremoved and replaced with a cannula. The cannula is ideally dimensionedfor providing an insertion path for positioning a biocompatible vehiclecontaining biologically active factors at the desired treatment site.The guidewire is removed, and the vehicle is inserted into the cannulaand guided along the passageway of the cannula towards the treatmentsite. Once the vehicle is positioned near the distal end of the cannula(i.e. at the treatment site), the cannula is removed from thepassageway, leaving the vehicle at the treatment site.

A pusher can be inserted into the cannula after the vehicle is initiallyplaced in the cannula so as to aid in positioning the vehicle at thedistal end. As above, this may be necessary if, for example, the vehicledoes not slide freely within the lumen of the cannula.

In another form of the invention, the insertion site is enlarged byintroducing at least one dilator over the guidewire before the insertionof the cannula.

In another form of the invention, the cannula is filled with aphysiologically compatible solution following removal of an obturator ora dilator and prior to inserting the vehicle. In this manner, the fluidserves as a lubricant to assist in positioning the vehicle at the distalend of the cannula.

The vehicles used in practicing the method of the invention, includecapsules containing biologically active factors. These capsules mayinclude an integral tether that extends from the capsule. The tetherpreferably is of a length sufficient to reach at least from thetreatment site to the proximity of the insertion site. The tether mayalso be a part of the cell capsule itself that extends above theinsertion site. In addition, the tether may form a secondary seal on thecapsule. Once the vehicle capsule is positioned in the passageway to thetreatment site, the tether may then be secured at the insertion site,e.g., by securing the tether to the outer surface of the skull proximalto the insertion site by means of surgical staples, biocompatibleadhesive, and the other methods available and known to those skilled inthe art. Following positioning of the vehicle at the treatment site, theinsertion site may be closed or capped to prevent introduction ofextraneous material to the passageway and the treatment site.

In one aspect of the invention, the vehicle may include an amount of adetectable marker, such as a radio-opaque material, to facilitate insitu monitoring of the vehicle at the treatment site. The vehicle maythen post-operatively be monitored in the patient through the use of CATscan, MRI or the like.

Systems for providing encapsulated biological material to a selectedtreatment site are also disclosed. A system that can be used to practicethe method of the invention includes a cannula, an obturator, and abiological vehicle. The cannula is adapted to receive the vehicle,having an open proximal end for receiving the obturator and the vehicle,and an open distal end for delivering the vehicle to the treatment site.The obturator is of the type designed for insertion within and along asubstantial length of the cannula to prevent backfill of materials, suchas dura, into the cannula during insertion of the cannula to thetreatment site. The obturator is also adapted to assist in positioningthe encapsulated neuroactive factors within the cannula.

Another system that can be used to practice the method of the inventionincludes a guidance needle, a guidewire, a cannula, and a biologicalvehicle. The guidance needle has a lumen adapted to receive theguidewire, such that the guidewire can be fed therethrough from an openproximal end adapted for receiving the guidewire to an open distal endwhich can be placed at or proximate the treatment site. The guidanceneedle is removable from the insertion site and disconnectable from theguidewire without affecting the guidewires ultimate position at thedesired treatment site. The cannula has a bore adapted for receiving thevehicle and the guidewire, having an open proximal end for receiving thevehicle, and an open distal end for delivering the vehicle to thetreatment site. The system can further include an obturator forreversibly blocking the lumen of the guidance needle, as well asdilators adapted for receiving the guidewire and slidable therealong. Apusher can also be used with the system, the pusher adapted for passingthrough the lumen of the cannula and pushing the vehicle to the distalend of the cannula.

The vehicles of the system of the invention can include a cell capsulehaving a biocompatible permselective outer membrane encapsulating cellscapable of releasing active factors. The vehicle generally has a shapewhich enables insertion within and movement along the cannula. In oneform, the vehicles are smooth, seamless capsules formed by extrusionthrough a multilumen spinneret. In that form, the capsules are formedfrom a biocompatible, permselective thermoplastic, encapsulating asuspension of cells that secrete a biologically active factor. Exemplaryclasses of active factors include neurotransmitters, neuropeptidesincluding opioid peptides, growth factors, trophic factors, andanalgesic factors such as catecholamines. In another form, the vehiclesare hollow fibers filled with the factor-secreting cells.

The vehicles of the present system further include a tether extendingfrom the capsule for securing the vehicle at the treatment sitefollowing insertion. The tether may be integral with the capsule, or maybe attached by methods available and known to those skilled in the art.

The term "biologically active factors" used herein includes:neurotransmitters such as gamma aminobutyric acid, serotonin,acetylcholine, , glutamic acid and dopamine; and neuroactive analgesicfactors such as catecholamines (e.g. epinephrine and norepinephrine) andopioid peptides. The term also includes precursors, agonists, activeanalogs, and active fragments of these neurotransmitters (e.g. dopamineprecursor L-dopa and dopamine agonist bromocriptine). Cells that secreteneuroactive factors such as peptide neurotransmitters, growth factors,trophic factors, catecholamines, opioid peptides, and/or hormones mayalso be useful. These include: insulin, Factor VIII, trophic factorssuch as erythropoeitin and growth hormones, biological responsemodifiers such as lymphokines and cytokines, enzymes, and antibodiesfrom antibody-secreting cells, neuropeptides such as enkephalins,dynorphins, Substance P, Met-enkephalin, neuropeptide Y, vasoactiveintestinal polypeptide, neurotensin, somatostania, and endorphins,catecholamines such as epinephrine and norepinephrine, as well asfactors such as nerve growth factor (NGF), brain-derived neurotophicfactor (BDNF), neurotrophin-3 (NT-3), an array of fibroblast growthfactors, and an array of neurotrophic factors.

The term "semipermeable" is used herein to describe biocompatiblemembranes that allow the diffusion therethrough of molecules having arelatively low molecular weight, i.e., approximately 150 kD, whileexcluding the passage of those having a relatively high molecularweight.

In one embodiment of the invention, the semipermeable membrane of thereceptacle preferably contains pores having a molecular weight exclusionof about 150 kD. This membrane excludes the passage therethrough oflarge particles such as those which are capable of degrading theneurotransmitter or injuring the neurotransmitter-producing cells (e.g.viruses, antibodies, complement, and various proteases). Thesemipermeable membrane can be made of various polymeric compositionssuch as a polyvinylchloride, polyacrylonitrile, polyvinylidene fluoride,polystyrene, polyurethane, polyamides, cellulose acetates and nitrates,polymethylmethacrylate, polysulfones, polyacrylates including acryliccopolymers, and derivatives, copolymers, and mixtures thereof.

The encapsulated cells may include secretory cells which have beenisolated from natural sources, or have been genetically engineered toproduce neuroactive factors, growth factors or agonists, precursors,active analogs, or active fragments thereof. For example, chromaffincells of the adrenal medulla, embryonic ventral mesencephalic tissue,and various neuroblastic cell lines such as PC12 function to supplydopamine and other active factors, and therefore, are preferred forincorporation into the device. In some aspects of the invention, thecell is an allograft (i.e., cells from another of the same species asthe subject in which it is to be implanted) or a xenograft (i.e., cellsfrom another of a different species).

The invention will next be described in connection with certainillustrated embodiments. However, it should be clear that variousmodifications, additions, and subtractions can be made without departingfrom the spirit or scope of the invention. For example, the presentinvention should not be read to require, or be limited to, a particulardevice shape, material, neuroactive factors, growth factor, or cell linedescribed by way of example or illustration.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself can be more fully understood from the followingdescription when read together with the accompanying drawings in which:

FIGS. 1A-1G are a series of schematic drawings illustrating the steps ofan exemplary method of implanting a biological vehicle;

FIGS. 2A-2J are a series of schematic drawings illustrating the steps ofanother exemplary method of implanting a biological vehicle;

FIGS. 3A, 3B, 3C, 3D and 3E show various alternative designs forimplantable neurological therapy devices; and

FIG. 4 is a schematic illustration of an implantable neurologicaltherapy device according to the system of the present invention.

Like reference characters in the respective figures indicatecorresponding parts.

DETAILED DESCRIPTION

The invention disclosed herein concerns methods and systems for theconstitutive and controlled delivery of biologically active factors,such as neurotransmitters, neuroactive factors, fibroblast growthfactors and the like, as well as precursors, agonists, active fragments,and active analogs thereof, to a target treatment site within a patient.

FIGS. 1A-1G illustrate the steps involved in practicing an exemplarymethod of the present invention. Generally, the method involvessurgically exposing an insertion site 10 located above a desired,pre-determined treatment site 12. A cannula 20 is fitted with anobturator 30, and the cannula/obturator assembly 25 is inserted atinsertion site 10. The obturator 30 is then removed from within thecannula 20, and a biocompatible vehicle (40 in FIG. 1C) is inserted intothe cannula 20. Once the vehicle 40 is appropriately positioned, thecannula 20 is removed, leaving the vehicle 40 in position at thetreatment site 12.

Specifically, FIG. 1A illustrates the cannula 20, having an insertedobturator 30, positioned through the insertion site 10 to the targettreatment site 12. The obturator 30 preferably is a blunt-end obturatorto minimize or prevent tissue damage. This positioning of the cannula 20forms a passageway to the treatment site 12. The specific location ofthe insertion site is determined using a stereotaxic assembly includinga cannula mount 14 and an obturator mount 16. The mounts 14, 16 are usedto sterotaxically position the cannula 20 for accurate placement at thetreatment site 12. In a preferred embodiment, an isodiametricstereotaxic apparatus is used that is commercially available fromRadionics, Burlington, Mass.

The cannula 20 may be of any commercially available type. Generally, ithas an open proximal end 20a for insertion of the obturator 30 and theencapsulation cell vehicle 40. The cannula 20 also has an open distalend 20b for delivering the vehicle 40 to the treatment site. Inaddition, the cannula 20 includes a central bore 26, with asubstantially smooth interior surface. The distal end 20b may be blunt,rounded, or pointed, depending on the tissue structure into which itwill penetrate, the acceptable amount of ancillary damage, and othersuch considerations.

In one embodiment, the cannula 20 can be constructed ofpolytetrafluoroethylene (Teflon™) or similar low friction polymers tominimize the risk of abrasive damage to the vehicles during insertion.Specifically, a Teflon™ barrel featuring a gradual reduction of both theinside and outside diameters and a thinning of the cannula wall of thetip can be employed. Such low friction polymeric cannulae are moreeasily inserted into and removed from the brain (or other target site)and can be made to be transparent to permit monitoring of the progressof the vehicle through the cannula, and verification that there is noblood or debris in the cannula that could affect the vehicle'sbiocompatibility.

Polymers such as polytetrafluoroethylene not only minimize friction butalso assure that the encapsulated cell vehicle's surface is notcontaminated with metals or metal ions as it passes through the cannula.Finally, the "tapering" feature at the end of cannula 20 (caused by thereduced thickness of the distal end 20b) serves to verifyobturator/pusher clearance from the end of the cannula to eliminate thepossibility of over, or under, driving the vehicle during insertion.

As shown in FIG. 1A, the cannula 20 is positioned at the treatment site12 with the obturator 30 inserted therein to prevent material, such asdura and the like, from entering the cannula 20 during insertion.Alternate methods and devices may be used to achieve similar results.

The next step, illustrated in FIG. 1B, involves removing the obturator30 from within the cannula 20. This may be achieved either by using theobturator mount 16, or manually. The cannula 20 remains at the treatmentsite 12, and is generally free of extraneous material along its centralbore 26.

The next step, illustrated at FIG. 1C, involves placing a cellencapsulation vehicle 40 at the treatment site 12. The vehicle 40 isgenerally of a predetermined shape to slidably fit within the centralbore 26 of the cannula. In a preferred embodiment, the vehicle 40 is atethered capsule containing biologically active factors. In thatembodiment, the vehicle 40 includes a capsule 42 containing thebiologically active factor, with a tether 44, or rod, extendingtherefrom. The tether 44 is of a length sufficient to reach from thecapsule 42, at the treatment site 12, to a location external to theinsertion site 10, and may be an extension of the cell vehicle.

In one form of the inventive method, prior to inserting the vehicle 40,the central bore 26 of the cannula is filled with a physiologicallycompatible solution, such as sterile saline. The vehicle 40 is theninserted within the cannula, and the solution acts as a lubricant toassure passage of the vehicle to the distal end 20b of the cannula.

Alternatively, and as illustrated in FIG. 1D, following insertion of thevehicle 40 within the cannula 20, a guide wire 32 may be inserted toassist in positioning the vehicle 40 at the distal end 24 of thecannula. The guide wire 32 may be either the same obturator 30 as thatinitially positioned within the cannula, a different obturator, a guidewire, or the like. The guide wire 32 is placed above the vehicle 40within the cannula, and the vehicle 40 is gently pushed into position atthe distal end 24 of the cannula.

Finally, the cannula 20 is removed from the treatment site 12, asillustrated in FIG. 1E. If a guide wire 32 or other device is used inthe preceding step to position the vehicle 40, generally that device 32is removed following the cannula 20. As with the obturator 30, thecannula 20 may be removed either by the cannula mount 14 or manually.The end result is positioning of the vehicle 40 at the treatment site12.

If the vehicle 40 is a tethered capsule, the tether 44 may be securedadjacent the insertion site 10 by means of a surgical clip 60 or thelike, shown in FIG. 1F. In that, preferred form of the inventive method,the tether 44 allows the vehicle 40 to be retrieved from the treatmentsite 12. As a final, optional step, a cap 62 may be used to seal theinsertion site 10 to prevent introduction of extraneous material throughthe insertion site (FIG. 1G).

The method described above is well suited for implantation ofencapsulated cells into the brain, but may be used to introducebiologically active factors to other structures and organs. Inpracticing the inventive method, multiple vehicles may be required oneach side of the patient's brain. Each vehicle is inserted in the samefashion, as described above. An initial scan, such as a CAT scan, may beperformed on the patient to determine the precise location of thetreatment site. For example, in treating Parkinson's disease, the basalganglia, specifically the substantia nigra, is identified as thetreatment site.

FIGS. 2A-2J illustrate the steps involved in practicing anotherexemplary method of the present invention, which is particularly wellsuited for intraspinal implantation of encapsulated cells, especiallyintrathecal implantation of encapsulated cells within the subarachnoidspace of the spinal column, or other treatment sites where initial entryis better gained by the use of a needle or cannula of smaller diameterthan ultimately needed to introduce the biological vehicle. Generally,the method involves surgically exposing an insertion site 10' locatedabove a desired, predetermined treatment site 12'. Where thepredetermined treatment site 12' is the subarachnoid space (116 in FIG.2J), an incision can be made over the interspace of two vertebrae 110,such as between the L-3 and L-4 vertebrae, in a manner similar to thepreparation needed for administration of a lumbar anesthetic. A guidanceneedle 100 is introduced into the insertion site and the distal end 100Bof the guidance needle 100 is located at or proximate to the treatmentsite 12'. A guidewire 102 is inserted down the lumen 101 of guidanceneedle 100 such that the distal tip 103B of guidewire 102 is alsolocated at or proximate the treatment site 12'. The guidewire 102 andguidance needle 100 are so dimensioned that the guidance needle 100 canbe withdrawn from the treatment site 12' without significantly alteringthe position of the distal end 103B of guidewire 102 relative to thetreatment site 12'. Further, the proximal end 103B of guidewire 102 isdimensioned so that guidance needle 100 can be withdrawn free ofguidewire 102. A cannula 20 can then be directed along guidewire 102such that its distal end 20B is positioned at the treatment site 12'.The guidewire 102 is then withdrawn from the central bore 26 of cannula20, and a cell capsule vehicle 40 is inserted into the cannula 20. Oncethe vehicle 40 is appropriately positioned, the cannula 20 is removed,leaving the vehicle 40 in position at treatment site 12'. Where desired,a dilator 104 can be introduced along the guidewire prior to orconcomitant with the insertion of the cannula. The dilator 104 can beused separately to expand the insertion site, as well as used with thecannula 20 to act as an obturator and improve the guidance of thecannula 20 along the guidewire 102.

Specifically, FIG. 2A illustrates the guidance needle 100 positionedthrough an insertion site 10' so that its distal tip 100B is located ator proximate the target treatment site 12'. If desired, the guidanceneedle 100 can also include a removable obturator (not shown) positionedin its lumen 101. As illustrated in FIG. 2J, in the instance where thetreatment site 12' is in the subarachnoidal space 116, the guidanceneedle 100 can be a Tuohy needle or similar needle thereto. By way ofillustration, the Tuohy needle is introduced between the L-3 and L-4vertebrae 110 with the open side of the needle facing the head (i.e.,curved portion of the needle caudal) at a 30°-40° angle, through theligamentum flavum 112 and epidura 114 and into the subarachnoid space116. If desired, a sample of fluid can be removed through the guidanceneedle and tested for the presence of cerebral spinal fluid (CSF), usingassays such as the determination of glucose levels in the fluid (e.g. aglucose level near 100 mg/dL is indicative of CSF).

As illustrated by FIG. 2B, once the guidance needle 100 is located atthe treatment site 12', a guidewire 102 is fed through the lumen 101 ofthe needle 100 so that the distal end 103B of guidewire 102 is alsolocated at or proximate to the treatment site 12'. If the needle 100 hasan obturator, the obturator is removed to provide an open lumen 101 forpassage of guidewire 102. The guidewire 102 is so dimensioned that itcan pass through the lumen 101 of needle 100, from the needle's proximalend 100A to its distal end 100B, such that, as shown in FIG. 2C, needle100 can be removed entirely from the treatment site 12', leaving theguidewire 102 in place and free of needle 100.

If desired, the insertion site can be enlarged by introducing at leastone dilator 104 over the guidewire 102. As illustrated by FIG. 2D,dilator 104 is introduced through the insertion site and towards thetreatment site 12' by tracking the path of guidewire 102, with theguidewire passing through the bore 105 of dilator 104. Dilator 104 canbe used to increase the size of the insertion site to ultimatelyaccommodate a cannula of a given size. The dilator 104 is especiallyuseful for spreading apart tissue including muscle and cartilage as wellas spreading closely spaced bone, such as found when trying to penetrateto the subarachnoid space of the spinal column.

As illustrated in FIG. 2E, the cannula 20, having the final dilator 104housed within its central bore 26, can then be introduced over theguidewire, and its distal end 20B positioned at the treatment site 12'for the introduction of the biological vehicle 40. Having a dilatordisposed within the cannula 20 serves a number of useful purposesincluding keeping the bore 26 of cannula 20 substantially free fromtissue (e.g. dural matter) upon insertion, as well as providing betterguidance by virtue of the guidewire 102 being passed through the smallerdiameter bore 105 of dilator 104 rather than the larger bore 26 ofcannula 20. However, it is clear that any intermediate steps ofdisposing dilators along guidewire 102 are not required, and that, ifdesired, the cannula 20 can be disposed directly along the guidewire 102without use of any dilators. The cannula 20 illustrated in FIGS. 2A-2Iis substantially identical to that illustrated in FIGS. 1A-1G, but neednot be adapted for use with a stereotactic frame. Additionally, wherethe insertion path is not a straight line, the cannula may be curvedsimilarly to the guidance needle.

The next step, illustrated in FIG. 2F, is to remove the guidewire andany dilator that may be disposed in the bore 26 of cannula 20. Thus, thedistal end 20B of cannula 20 remains at the treatment site 12, and isgenerally free of extraneous material along its central bore 26.

The next step, illustrated at FIG. 2G, involves placing a cellencapsulation vehicle 40 at the treatment site 12'. Similar to themethod illustrated in FIGS. 1A-1G, the vehicle 40 is generally of apredetermined shape to slidably fit within the central bore 26 of thecannula 20. In a preferred embodiment, the vehicle 40 is a tetheredcapsule containing biologically active factors. In that embodiment, thevehicle 40 includes a capsule 42 containing the biologically activefactor, with a tether 44, or rod, extending therefrom. The tether 44 isof a length sufficient to reach from the capsule 42, at the treatmentsite 12', to a location external to the insertion site 10', and may bean extension of the cell vehicle.

In one form of the inventive method, prior to inserting the vehicle 40,the central bore 26 of the cannula 20 is filled with a physiologicallycompatible solution, such as sterile saline. The vehicle 40 is theninserted within the cannula, and the solution acts as a lubricant toassure passage of the vehicle to the distal end 20B of the cannula.

Alternatively, and as illustrated in FIG. 2H, following insertion of thevehicle 40 within the cannula 20, a pusher 106 may be inserted to assistin positioning the vehicle 40 at the distal end 20B of the cannula. Thepusher 106 may be either an obturator dimensioned for the cannula 20, aguide wire, or the like. The pusher 106 is placed above the vehicle 40within the cannula, and the vehicle 40 is gently pushed into position atthe distal end 20B of the cannula 20.

Finally, the cannula 20 is removed from the treatment site 12', asillustrated in FIG. 2I. If a pusher 106 or other device is used in thepreceding step to position the vehicle 40, generally that device isremoved following the cannula 20 to ensure that the vehicle 40 remainsat treatment site 12' and is not accidentally moved with the withdrawalof the cannula 20.

In one particular embodiment, the system of this invention comprises: an18 gauge, 4 inch long Tuohy needle with styler and hub (Popper & Sons);a 0.032 inch×31 inch flexible guide wire (Lake region, Act modified); a7-French vessel dilator (#392306, Argon Medical); a 6-French 30cmdilator and TEFLON sheath with stopcock removed (Angestat HG06-0,Angeion) where the sheath corresponds to the cannula 20 and the 6Fdilator corresponds to the dilator 104 in FIG. 2E; a pusher having a0.054"×187 mm wire pusher (with a 255 mm handle); and a biologicalvehicle comprising bovine or porcine adrenal chromaffin cells suspendedin an alginate matrix and encapsulated in a PAN/PVC capsule (750 μmID×950 μm OD×5 cm; 25μl volume) with a 195 mm occluded lumen siliconetether (Speciality Silicone Fabricators).

In FIGS, 1A-1G and 2A-2I, the vehicle 40 has the shape of a rod.However, it should be appreciated that the vehicle 40 may have any shapewhich can accommodate the source of biologically active factor, or cellswhich release active factors, without causing undue trauma to thepatient during implantation. The present immunoisolatory vehicle can beformed in a wide variety of shapes and combinations of suitablematerials. A primary consideration in selecting a particularconfiguration for the vehicle when cells are present is the access ofoxygen and nutrients to the isolated cells or tissues, and passage ofwaste metabolites, toxins and the secreted product from the vehicle. Theinstant vehicle must provide, in at least one dimension, sufficientlyclose proximity of any isolated cells in the core to the surroundingtissues of the recipient, including the recipient's bloodstream, inorder to maintain the viability and function of the isolated cells. Ingeneral, the vehicle will have a maximum depth-to-surface distance of nomore than 2 mm in at least one dimension, with a maximum depth of 500microns being preferred. One or several vehicles may be required toproduce the desired effect in the recipient.

In FIGS. 3A through 3E, several alternative embodiments of implantableimmunoisolatory vehicles are shown. In FIG. 3A, polymeric capsule 80A(which can have an open end) containing active factor secreting cells isjoined to hollow tether 82. The distal end of the hollow tether 82 inFIG. 3A can be plugged, e.g., filled with a plug 84 or chitosan or thelike, and the proximal end can be closed by sealing clip 60. In FIG. 3Ba closed polymeric capsule 80B similarly containing active factorsecreting cells can be simply sealed to a solid tether 86. In FIG. 3C, acell capsule 80C having polyurethane sealed ends is joined to anotherhollow fiber 82. In FIG. 3D, a cell capsule 80D having one end that isintegrally sealed and the other end plugged (e.g. with polyurethane) isjoined to a solid tether 86. Finally, in FIG. 3E, yet another embodimentis shown comprising an open cell capsule 80E sealed with polyurethane 88at its distal end and joined to a hollow tether 82 at its other(proximal) end. The hollow tether 82 uses a hyaluronic acid plug 90 tohold the cells in place and is sealed at its proximal end by clip 60.

It should be clear that various other alternative vehicles can beconstructed. The cell capsules can be integrally sealed or plugged withvarious materials. Likewise, the tethers can be solid or hollow and canbe joined to the cell capsules by glues, friction fitting, fusion or thelike. The important factor is to construct a device that positions thecell capsules at a predetermined treatment site with sufficientstructural integrity to achieve such placement as well as removalintact, if desired at a later date.

In one preferred embodiment, the implantable immunoisolatory vehicle ofthe present invention is of a sufficient size and durability forcomplete retrieval after implantation. To be contrasted with suchmicrocapsules, which have a typical maximum practical volume on theorder of 1 μl, the preferred immunoisolatory vehicle of the presentinvention is termed "macrocapsule". Such macrocapsules have a core of apreferable minimum volume of about 1 to 10 μl and depending upon use areeasily fabricated to have a value in excess of 100 μl. To increase thetherapeutic value provided by tissue encapsulated in microspheres, thenumber of microspheres must be increased to such a large extent thatsignificant retrievability becomes impossible. Additionally, an increasein the volume of tissue placed within a microsphere requires acorresponding increase in surface area. Within a sphere, because surfacearea scales with r² where as volume scales with r³, as the volume ofencapsulated tissue volume increases, the required capsule size toprovide sufficient surface area for nutrient diffusion quickly becomesimpractical. Macrocapsules in the shapes of cylinders or flat sheets donot have these limitations because volume increases more proportionatelyto surface area such that the diffusional transport of nutrients andproducts for increased mounts of tissue can be accommodated byincreasing the surface area without unwieldy increases in total vehiclesize.

The encapsulated cell vehicle 40, shown in further detail in FIG. 4,includes capsule 42 filled with a secretory cell, preferably a cell thatproduces biologically active factors. In a preferred embodiment, thecapsule 42 includes a tether 44 or rod extending from and integral withthe capsule. The vehicle further includes a permeable, semi-permeable,or permselective membrane surrounding the capsule 42. The tether 44 isgenerally constructed from an impermeable membrane material or may becoated with a material which makes the tether impermeable. In oneembodiment, the impermeable protective barrier material may coat aportion of the outer membrane of the capsule. Exemplary protectivebarrier material includes polyethylene oxides, polypropylene oxides,silicon, hydrogels, and derivatives and mixtures thereof. It should beappreciated that the semipermeable membrane may have alternative shapesthat will accommodate the cells such as, for example, a hollow rod,sack, or multiple fibers.

The outer membrane may be a polymer material and may include asurfactant, an anti-inflammatory agent, angiogenic factors, and/or ananti-oxidant. The specific type of polymer, surfactant, or otheradditive will depend on the material to be encapsulated and theconfiguration of the extrusion apparatus. Exemplary anti-inflammatoryagents include corticoids such as cortisone and ACTH, dexamethasone,cortisol, interleukin-1 and its receptor antagonists, and antibodies toTGF-β, to interleukin-1 (IL-1), and to interferon-gamma. Exemplarysurfactants include Triton-X 100 from Sigma Chemicals, and PluronicsP65, P32, and P18. Exemplary anti-oxidants include vitamin C (ascorbicacid) and vitamin E. Exemplary angiogenic factors include fibroblastgrowth factor and nerve growth factor.

In the event that the supply of active factors, e.g., cells secretingsuch factors, is spent, the vehicle can be removed and replaced.Retrieval of implanted vehicle 40 can be accomplished by pulling it outof the treatment site by its tether 44. One way to effect removal is touse a pair of forceps after exposing the tether 44 by removal of the cap62. Cap 62 may be located directly under the patient's epithelialtissues. The vehicle 40 may be replaced with a new insert in the eventthat additional therapy is required. Cells encapsulated within capsule42 (FIG. 4) can also be retrieved if the cells cease to produce thebiologically active factor, expire, or are no longer needed to correctthe particular dysfunction.

The permeable portion (e.g., capsule 42) of vehicle 40 is implanted ator near the target treatment site 12, while the impermeable portion(e.g., tether 42) confines the neuroactive factor to within theboundaries of the insert. The permeable portion includes a polymericmaterial having pores of a particular size (i.e., having a particularmolecular weight cut-off) that excludes some molecules from passagetherethrough, while permitting the passage of others. In this way, thediffusion of neurotransmitter from the insert to the treatment site isallowed, while the passage of larger deleterious elements such asviruses, Clq component complement, and various proteases is effectivelybarred. For example, vehicles with pores having a molecular weightexclusion of from about 50 kD to about 300 kD are useful, with thosehaving pores with a molecular weight cut off of from about 25 kD toabout 200 kD being particularly preferred.

The vehicle may be composed of any biocompatible material having thedesired pore size and being composed of materials which do not limit theactivity of the substance embedded therein. Hydrophilic matrices such ashydrogels (e.g., hydroxyethyl methacrylate, polyanhydrides, polyvinylalcohol, and polyvinyl pyrrolidone) and hydrophobic matrices such asethylene vinyl acetate are particularly useful.

The vehicle 40 can provide any biologically active factor which willsatisfy the subject deficiency or remedy the dysfunction. These includegamma aminobutyric acid, serotonin, acetylcholine, epinephrine,norepinephrine, dopamine, enkephalins, and endorphins. Alternatively,the device may provide an active analog, active fragment, or activederivative of the neuroactive factor, or may include a precursor which,after processing, provides the same activity as the factor in theappropriate in vivo location. The device may further include an agonistof the factor. Other agents may include insulin, Factor VIII, trophicfactors such as, erythropoeitin and growth hormone, biological responsemodifiers, such as lymphokines and cytokines, enzymes, and antibodiesfrom antibody-secreting cells. In addition, the capsule may containmultiple cell-types and cells, tissue, or other appropriate substance.

An exemplary form of the vehicle 40 is a smooth, seamless vehiclemanufactured by coextrusion of a polymeric casting solution and a cellsolution. In this approach a multi-bore extrusion nozzle is used withthe polymeric solution extruded from the outer bore and the cellsuspension coextruded from an inner bore. In addition to containingcells of tissue of the type described above, the cell suspension mayinclude nutrients, such as fetal bovine, equine or porcine serum.

Any cells which secrete the biologically active factor that istherapeutic to the subject malady may be incorporated into the system ofthe invention. For example, the cells may be any which naturally producea neurotransmitter, such as neurons. Such cells are useful because theyare able to respond to the general environment by producingneurotransmitter as it is needed. Further, cells can be obtained from anumber of sources such as body organs which normally secrete aparticular factor in vivo. For example, tissues of the embryonic ventralmesencephalon and adrenal medulla (chromaffin cells) which normallyproduce dopamine can be used. These tissues may be an allograft or axenograft. Alternatively, the cell may be derived from various culturedcell lines, such as PC12.

Where the intended transplantation site is a CNS pain modulatory regionwith the end goal of decreasing nociception, the encapsulation ofadrenal medullary tissue and more particularly, chromaffin cells, of theadrenal medulla, may be desirable. In addition to dopamine, chromaffincells release several other neuroactive and substances, includingcatecholamines and opioid peptides, which can reduce pain sensitivitywhen administered directly into the spinal cord. (Sagen et al. (1991) J.Neurochem 56: 623-627; Sagen et al. (1986) Brain Res. 384: 189-194; andSagen et al. (1990) Pain 42: 69-79, incorporated by reference herein).

Various "growth factors" having the ability to stimulate cell growth,differentiation, and/or factor secretion may be co-implanted with theactive factor-secreting cells to insure successful delivery of thedesired agent or factor to the treatment site. These growth factors maybe specific for a cell type or have a generalized effect on a number ofdifferent tissues. In the case of neurotransmitter-producing cells suchas neurons, growth factors can act to maintain neurotransmitterproduction, as well as to promote cell maintenance and growth.Alternatively, growth factors may maintain nerve cells in adifferentiated state. Useful cell growth factors include nerve growthfactor (NGF), an array of fibroblast growth factors (FGF),platelet-derived growth factor (PDGF), brain-derived neuroprophic factor(BDNF), and epidermal growth factor (EGF), and ciliary growth factor,among many. In addition, effectors of various membrane receptors such asglutamate and nicotine may also be useful.

In addition, any cell which secretes a precursor, agonist, activeanalog, or active fragment of a desired biologically active factor orgrowth factor having similar therapeutic activity can also be used. Forexample, cells which elicit L-dopa, a precursor of dopamine, orbromocriptine, a dopamine agonist may be used in the treatment ofParkinson's disease.

Further, any cells which have been genetically engineered to express adesired neuroactive factor, growth factor, or their agonists,precursors, derivatives, analogs, or fragments thereof, or other activefactors having similar effector activities are also useful in practicingthis invention. Thus, in such an approach, the gene which encodes theneuroactive factor, or its analog or precursor is either isolated from acell line or constructed by DNA manipulation. The gene can then beincorporated into a plasmid which, in turn, is transfected into a cell,such as a fibroblast, for expression. (See, e.g., Sambrook et al.,Molecular Cloning (1989), herein incorporated by reference for furtherdiscussion of cloning vehicles and gene manipulation procedures.) Thecells which express the biologically active factor or factor can begrown in vitro until a suitable density is achieved.

Alternatively, growth factor-producing cells such as hippocampal cellsor fibroblasts engineered to produce NGF (see e.g., Rosenberg et al.(1988) Science 242:1575-1578) may be encapsulated and implanted inproximity to the factor-secreting cells as described above.

By the term "biocompatibility" is meant that the functioning of thevehicle is not impeded by the various protective systems of the host.This includes a failure to elicit a detrimental foreign body/fibrosisresponse. The vehicle is also preferably substantially free of localcytotoxic effects, i.e., free of leachable pyrogens. In a preferredform, a seamless tethered capsule is used as the vehicle. In embodimentsemploying seamed capsules, the number and size of the seams arepreferably minimized, and the vehicle has smooth surfaces without edgesor villi. Although many forms of tether may be attached, preferredtethers are continuous with the capsule.

The system of the invention, useful for practicing the inventive methodas described above, includes a cannula, at least one obturator, and abiological vehicle. Each of these is substantially as described above.

In one particular aspect of the invention, a method of treatingParkinson's disease by neural implant has been developed. The cells canbe cells from primary cultures or cell lines that secrete dopamine andother active factors. Typical factor-secreting primary cells includeadrenal chromaffin cells, and neurons from the fetal substantia nigra. Asuitable cell line is the PC12 line. Additionally, geneticallyengineered fibroblasts or other cell types may be used. Prior to use,cells are cultured by standard techniques appropriate for the cell typeused.

In another aspect of the invention, a method and system foradministering antinociceptive agents to alleviate pain have beendeveloped. The encapsulated material can be tissue or cells able tosecrete such antinociceptive agents as catecholamines and opioidpeptides. Typically, the encapsulated material can be tissue of theadrenal medulla, or more particularly, adrenal medulla chromaffin cells.Additionally, genetically engineered cell lines or naturally othernaturally occuring cell lines able to secrete at least one pain reducingagent such as a catecholamine, opioid peptide, or agonist analogsthereof, can be used.

In one preferred embodiment, the capsule used is a thermoplastic PAN/PVCcapsule with a liquid and cell core, having a wall thickness of greaterthan 25 microns. The core may also contain a hydrogel matrix or thelike. The hydrogel matrix may be any commercially availablethree-dimensional network of hydrophilic polymers that are eithercovalently or ionically cross-linked. Any method of thermoplasticcapsule preparation may be used, including hollow fiber preparationfollowed by filling with the cells and plugging and sealing using heatsealing. Alternatively, the capsules can be formed by coextrusionthrough a multi-lumen spinneret.

The inclusion of a tether to the biocompatible vehicle should not affectcapsule functioning or its biocompatibility. The entire length of theexemplary vehicle, including the tether, typically is 8-10 cm. Methodsof tether manufacture include coextrusion through a multi-lumenspinneret. Other methods include the addition of a biocompatible sutureprotruding from the sealed capsule. Another form includes a hollowimmunoisolatory fiber of 80-100 mm in length containing, at one end, acell growth chamber of 10-20 mm with an internal plug. To produce asturdy, non-porous tether, the remainder of the fiber is dipped in apotting elastomer, such as polyurethane or polysilicon, preferably priorto loading the cells. In other forms, elastomeric tubing may be attachedto the capsule.

Although illustrated specifically for cranial insertion in FIG. 4, thevehicles of the present invention can also be inserted into otherregions of the body. For example, for pain relief applications thevehicles can be inserted into the sacral/lumbar regions of the spine toprovide encapsulated cells such as adrenal chromaffin cells whichsecrete enkephalins and/or catecholamines.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. A system for delivering a biologically activefactor to a selected treatment site in a subject, comprising:i) a singlecannula adapted for penetration through tissue into a selected positionin proximity with the treatment site, having a bore with a substantiallysmooth interior surface running axially therethrough through which avehicle may slidably move, an open, proximal end into which the vehiclemay be slidably inserted and a distal end having an opening throughwhich the vehicle may slidably move wherein the external diameter andbore diameter are tapered toward the distal tip; ii) an obturatordisposable within the cannula to prevent tissue material from enteringthe distal end of the cannula when it is inserted into tissue; iii) avehicle which encapsulates the biologically active factor, the vehiclehaving an outer surface which comprises a biocompatible semipermeableouter membrane through which the biologically active factor may bereleased into the selected treatment site, and a shape which enablesslidable insertion into the proximal end of the cannula, slidablemovement along the bore of the cannula, slidable passage through thedistal end of the cannula by removal of the cannula from the proximityof the treatment site; and iv) a pusher disposable within the cannula toengage the outer surface of the vehicle, to slidably move the vehiclethrough the bore, and to hold the vehicle in place at the selectedtreatment site when the cannula is removed from the proximity of thetreatment site, the pusher being removable after the vehicle ispositioned at the treatment site.
 2. The system of claim 1, furthercomprising:i) a guidance needle having a lumen running axiallytherethrough and being insertable into proximity with the treatmentsite; ii) a guidewire insertable into proximity with the treatment siteand able to pass completely through the lumen of the guidance needle;wherein the cannula is adapted to receive the guidewire and wherein thelumen of the guidance needle has a first open end for receiving theguidewire, and a second open end for passage of the guidewire to thetreatment site, the guidance needle being fully removable afterinsertion of the guidewire to the treatment site without disturbing theproximity of the guidewire to the treatment site, and the guidewirebeing able to guide the insertion of the cannula to the treatment site.3. The system of claim 2, further comprising at least one dilatordisposable along the guidewire to enlarge a pathway through which thecannula is inserted, the dilator having a dilator bore running axiallytherethrough and able to pass the guidewire therein.
 4. The system ofclaim 3, wherein the guidance needle has a beveled, curved tip.
 5. Thesystem of claim 2, further comprising at least one obturator forinsertion within and along the lumen of the guidance needle to preventbackfill of materials into the guidance needle during insertion of theguidance needle, the obturator being fully removable after insertion ofthe guidance needle into proximity with the treatment site.
 6. Thesystem of claim 1, wherein at least a portion of the proximal end of thecannula is transparent to permit monitoring the progress of the vehicleduring insertion into the cannula and during passage through thetransparent portion of the cannula.
 7. The system of claim 1, whereinthe distal end of the cannula is rounded to reduce ancillary tissuedamage, and wherein the active factor comprises at least one neuroactivefactor selected from the group consisting of peptide neurotransmitters,growth factors, trophic factors, catecholamines, opioid peptides andhormones.
 8. The system of claim 1, wherein the system is adapted fordelivering the vehicle into a human spinal region, and wherein thevehicle releases at least one antinociceptive agent useful in atreatment for pain relief.
 9. The system of claim 1, wherein the vehicleencapsulates cells that secrete the biologically active factor.
 10. Thesystem of claim 9, wherein the encapsulated cells comprise adrenalmedullary chromaffin cells.
 11. The system of claim 9, wherein thedistal end of the cannula is rounded to reduce ancillary tissue damage,and wherein the active factor comprises a neuroactive factor selectedfrom the group consisting of peptide neurotransmitters, growth factors,trophic factors, catecholamines, opioid peptides and hormones.
 12. Thesystem of claim 1, wherein the vehicle further comprises an impermeableprotective barrier material which coats a portion of the outer membrane.13. The system of claim 1, wherein the cannula is constructed frommaterial comprising a low friction polymer.
 14. The system of claim 13,wherein the polymer comprises polytetrafluoroethylene.
 15. The system ofclaim 1, wherein the active factor comprises at least oneantinociceptive agent useful in a treatment for pain relief.
 16. Thesystem of claim 1, wherein the cannula is flexible for the delivery ofthe vehicle through a curved pathway.
 17. A method for delivering abiologically active factor to a selected treatment site in a subject,comprising:i) surgically opening an insertion site located near theselected treatment site; ii) inserting a single cannula adapted forpenetration through tissue and an obturator disposed therein into theinsertion site and placing the distal end of the cannula at a selectedposition in proximity with the treatment site, the cannula having a borewith a substantially smooth surface running axially therethrough throughwhich a vehicle may slidably move, an open, proximal end into which thevehicle may be slidably inserted and a distal end having an openingthrough which the vehicle may slidably move wherein the externaldiameter an bore diameter are tapered toward the distal tip; iii)removing the obturator from the cannula; iv) introducing within the boreof the cannula a vehicle which encapsulates the biologically activefactor, the vehicle having an outer surface which comprises abiocompatible semipermeable outer membrane through which thebiologically active factor may be released into the selected treatmentsite, and a shape which enables slidable insertion into the proximal endof the cannula, slidable movement along the bore of the cannula,slidable passage through the distal end of the cannula by removal of thecannula from the proximity of the treatment site; v) delivering thevehicle to the distal end of the cannula with a pusher disposable withinthe cannula to engage the outer surface of the vehicle, to slidably movethe vehicle through the bore, and to hold the vehicle in place at theselected treatment site when the cannula is removed from the proximityof the treatment site; vi) removing the cannula from the tissue, whileleaving the vehicle inserted at the treatment site; and vii) removingthe pusher from the tissue.
 18. The method of claim 17, furthercomprising before a step of inserting the cannula,i) inserting aguidance needle having a lumen running axially therethrough intoproximity with the treatment site; ii) inserting a guidewire through thelumen of the inserted needle and into proximity with the treatment site,the guidewire able to pass completely through the lumen of the guidanceneedle; and iii) removing the guidance needle from the treatment sitewithout disturbing the proximity of the guidewire to the treatment site;wherein the cannula is adapted to receive the guidewire and wherein thelumen of the guidance needle has a first open end for receiving theguidewire, and a second open end for passage of the guidewire to thetreatment site, the guidance needle being fully removable afterinsertion of the guidewire to the treatment site without disturbing theproximity of the guidewire to the treatment site, and the guidewirebeing able to guide the insertion of the cannula to the treatment site.19. The method of claim 18, further comprising disposing, after removingthe guidance needle, at least one dilator along the guidewire andtowards the treatment site to enlarge a pathway through which thecannula is inserted, the dilator having a dilator bore running axiallytherethrough and able to pass the guidewire therein, the dilator beingremoved before the cannula is removed.
 20. The method of claim 18,further comprising, before a step of inserting the guidewire, disposingat least one obturator in the lumen of the guidance needle, theobturator of the type designed for insertion within and along the lumenof the guidance needle to prevent backfill of materials into theguidance needle during insertion of the guidance needle into proximitywith the treatment site, the obturator being removed before theguidewire is inserted.